Method of producing an oil bearing stratum of a subterranean formation in a steeply dipping reservoir



March 17, 1970 B. M. FITZGERALD 3,500,915

METHOD OF PRODUCING AN OIL BEARING STRATUM OF A SUBTERRANEAN FORMATION m A STEEPLY DIPPING RESERVOIR Filed Sept. 1:5, 1968 #07" WA 7' E f? 0/4 P14 0006 770A JTE/IM f p an...

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United States Patent 3,500,915 METHOD OF PRODUCING AN OIL BEARING STRATUM OF A SUBTERRANEAN FORMA- TION IN A STEEPLY DIPPING RESERVOIR Benny M. Fitzgerald, Bakersfield, Califi, assignor to Tenneco Oil Company, Houston, Tex., a corporation of Delaware Filed Sept. 13, 1968, Ser. No. 759,708 Int. Cl. E21b 43/24 US. Cl. 166-272 1 Claim ABSTRACT OF THE DISCLOSURE A method of producing an oil bearing stratum of a subterranean formation penetrated by first and second injection wells. The method includes the steps of generating steam of less than 100% quality, separating the hot water therefrom and injecting it into the formation and simultaneously injecting the separated substantially 100% quality injection steam into another part of the formation and producing hydrocarbon fluids from the heated stratum.

This invention relates to a method of producing an oil bearing stratum of a subterranean formation by application of heat thereto. More particularly, the invention relates to a method of producing the oil bearing stratum by heating the stratum by the use of both steam and hot water, wherein the hot water is derived from a steam of less than 100% quality.

In the production of certain hydrocarbon fluids such as high viscosity oils, it has been common practice to inject hot fluids into the formation in order to reduce the viscosity thereof such that the hydrocarbon fluids may be produced from the formation. It has been generally recognized that the more viscous the crude oil is, the greater will be the proportionate reduction in viscosity for a given temperature increase. This particular feature makes several recovery methods attractive. Steam injection has long been one favorite method of accomplishing such heat injection. The book entitled Mechanics of Secondary Recovery by Charles Robert Smith, published by Reinhold Publishing Corporation of New York, in 1966, particulaly in chapter 12 thereof, relates the various prior art methods and state of the art with respect to steam injection.

Heretofore, most steam injection projects have utilized 80% quality steam, i.e. steam which contains 80 weight percent saturated vapor, with the remainder being liquid. Steam of this quality has heretofore been injected into an oil bearing formation. However, steam of this quality is not as efiicient as is desired for various reasons. Further, the solids contained in the feed water are injected into the well in critical areas where it is better to have steam only. In some instances, separation at the outlet of a steam generator has been practiced and only the 100% quality steam injected into the reservoir. In these cases, the removed water or condensate is returned to the plant to preheat the inlet water. Hence, the heat contained in the separated water is not completely utilized in the reservoir, resulting in less optimum operations. Further, if 80% quality steam is injected into a reservoir, there is no assurance that either the liquid or the vapor phase will enter any specific horizon or portion of the formation. If 100% quality steam is injected into a reservoir by itself, it often develops that only the high permeability streaks therein will receive the vapor steam.

It is therefore an object of this invention to improve upon the natural driving forces in a reservoir, during removal of oil or hydrocarbon fuels from the reservoir, by

3,500,915 Patented Mar. 17, 1970 separate injection of steam and the condensate therefrom into the most advantageous portions of the reservoir.

It is a further object of this invention to provide an improved method for producing oil from an oil bearing stratum wherein the liquid phase of steam of less than quality is injected into the formation near the lower end of the oil bearing stratum and the vapor phase is injected into the formation near the upper portion of the oil bearing stratum.

Briefly stated, this invention is for a method of producing an oil bearing stratum of a subterranean formation penetrated by first and second injection wells extending into the formation at least to a point near the top of the stratum. The invention contemplates generating steam of less than 100% quality. The generated steam is then separated into a liquid phase and a vapor phase. The separated liquid phase is then passed down the first injection well and into the formation to thereby heat the oil hearing startum. Simultaneously, the separated vapor phase is passed down the second injection well and into the formation at a point spaced apart from liquid injection. Hydrocarbon fluids are then produced from the heated stratum.

Reference to the drawing will further explain the inven tion wherein:

FIG. 1 is a schematic side elevation view of a formation having an oil bearing stratum penetrated by two injection wells and one production well.

FIG. 2 is a schematic side elevation view of a steeply dipping reservoir having an oil bearing stratum therein, and showing a water injection well penetrating down structure from the oil bearing stratum and a steam injection well penetrating to a point up structure from the oil bearing stratum.

Referring now to FIG. I, initially, steam of less than 100% quality, i.e. steam having some amount of liquid therein, is produced in any conventional manner, as by a steam generator. A once-through type oilfield steam generator is suitable for the use to produce steam of less than 100% quality at a temperature of 450 F. and saturation pressure, for example. Thereafter, the hot water (liquid phase) is separated from the less than 100% quality steam by means of a separation vessel and is passed downwardly through injection well 11 which is shown penetrating to near the bottom of oil bearing stratum 12.

The substantially 100% quality steam (vapor phase) which results from the aforesaid separation is then simultaneously injected down injection well 13 and into the formation at a point near the top of oil bearing stratum 12. This injection of hot water and high quality steam is continued until stratum 12 is heated to the desired extent, thereby causing hydrocarbon fluids to become less viscous and flowable. By injecting the vapor phase into an upper portion of the oil bearing stratum, advantage is taken of natural forces occurring in the reservoir, i.e. bottom water drive, and gas cap expansion. Hence, by injecting the steam (vapor) and water (liquid) into the optimum zones of the stratum, the full driving forces of both the steam (vapor) and the hot water (liquid) are utilized.

The hydrocarbon fluids are then produced from stratum 12 through production well 14, which preferably penetrates to a lower portion thereof.

In some instances, the injection of the water (liquid phase) and steam (vapor phase) may be facilitated by fracturing the formation adjacent to the injection well. For example, the formation may be fractured as indicated by the numeral 15 at a point adjacent the injection well and at the desired elevation, which in the case of the vapor phase would be near the upper portion of the 3 tratum, and in the case of the liquid phase would be near be lower portion of the oil bearing stratum.

In the preferred embodiment of the invention, the vapor hase (steam) is injected into the upstructure wells of a lipping reservoir while the steam condensate (water) s injected into downstructure wells of the same reservoir. the injection wells may be reversed, but in any event the urpose of separating the two phases of the produced team is to obtain optimum efliciency in heating the oil ,nd reservoir rock. The vapor phase will move initially n the up-dip direction, while the liquid or condensate will nove in the down-dip direction. Oil heated by this method vill move into well bores provided for removal of the eservoir fluids.

The advantages of substantially 100% quality steam tre obtained in the method of this invention and the hot vater removed from the lower quality steam is utilized n the formation and not wasted or used in a less eificient nanner. Moreover, advantage is taken of the natural lriving forces, as stated above, to facilitate the producion of hydrocarbon fluids. The invention provides a method of injecting the vapor phase and the liquid phase nto controlled portions of the formation to obtain the lesired end results of eificient thermal recovery of hylrocarbon fluids.

FIG. 2. shows a steeply dipping reservoir having an oil tearing stratum 20 with gas bearing stratum 21 theretbOVfi, and a water bearing stratum 22 therebelow. In this nstance, it is desirable to have the water (liquid phase) njection well, in the form of well 24, penetrate to a point [own-structure from the oil bearing structure and steam vapor phase) injection well 25 penetrating to a point lp-structure from the oil bearing stratum, as shown.

In addition, oil bearing stratum 20 is penetrated by aroduction well 26 which preferably extends to a lower tortion thereof.

In the carrying out of the method of this invention n such a steeply dipping reservoir, the operations are nuch the same as with respect to the formation shown a FIG. 1. That is, steam of less than 100% quality is ;enerated. Hot water is then separated from the steam o produce an injection steam of substantially 100% uality. The separated hot water is passed down injection vell 24 and the separated injection steam is passed downvardly through injection well 25. The injection of both vater and steam causes heating of stratum in much the ame manner that stratum 20 in FIG. 1 is heated. Hydro- :arbon fluids are then produced in conventional manner rom production well 26.

It is to be understood that either of the injection wells may be fractured to facilitate passage of the respective fluids into the formation, the same as described with respect to FIG. 1.

Other advantages of this two phase injection system include:

(1) The solids contained in the feedwater will be separated with the condensate and would be injected into the reservoir near a water-oil contact or other less critical location. The vapor phase, then free of solids, could be injected into the reservoir as the main heating mechanism.

(2) The gravitational eifect on the liquid and vapor would be utilized to heat the reservoir and move fluids into the well bore.

Modifications may be made in the invention as described without departing from the scope of the invention. Accordingly, the foregoing description is to be construed as illustrative only and is not to be construed as a limitation upon the invention as defined in the following claim:

What is claimed is:

1. In a method of producing an oil bearing stratum in a steeply dipping reservoir in a subterranean formation penetrated by first and second injection wells, the combination of steps comprising:

generating steam of less than quality;

separating said steam into a liquid phase and a vapor phase;

passing said liquid phase down said first injection well and into said formation down-structure from said stratum to thereby heat said stratum;

passing said vapor phase down said second injection well and into' said formation up-structure from said stratum to thereby heat said stratum;

and, producing hydrocarbon fluids from said heated stratum.

References Cited UNITED STATES PATENTS 1,885,807 11/1932 Doherty l66268 X 3,358,759 12/ 1967 Parker l66271 X 3,421,583 1/ 1969 Koons 166-269 JAMES A. LEPPINK, Primary Examiner IAN A. CALVERT, Assistant Examiner US. Cl. X.R. 166-303 

